The overall objective of this proposal is to understand the cellular mechanisms underlying and regulating olfactory receptor neuron survival and differentiation. The olfactory bulb (OF) is known to exert dramatic regulatory control over olfactory receptor neuron (ORN) survival and differentiation. We hypothesize that contact with olfactory bulb cells is the event which triggers final functional differentiation of olfactory receptor neurons. this hypothesis will be tested by pinpointing the specific cellular and molecular changes, and cell-cell interactions that occur when olfactory epithelial (OE) cells are grown in the absence or presence of olfactory bulb cells, in dissociated cell culture monolayers. The principal investigator has developed cultures of newborn rat nasal tissues that contain electrically active ORNs that respond to odorants. Induction of olfactory marker protein (OMP) occurs if these cells are co- cultured with olfactory bulb astrocytes. These culture systems appear to be an excellent model for studies of olfactory system development. Specific Aim 1: Define the differentiated properties of olfactory receptor neurons in olfactory cell cultures grown in the absence of olfactory bulb cells. We will determine if ORNs which had previously contacted the olfactory bulb uniquely contain OMP or have different survival properties. We will determine if ORNs which had previously contacted the olfactory bulb uniquely contain IMP or have different survival properties. We will determine how closely coupled ORN survival is to changes in OMP expression. We will further define ORN electrophysiological properties. Specific Aim 2: Define the differentiated properties of olfactory receptor neurons grown in the presence of olfactory bulb cells. We will determine if OMP- positive neurons appear in co-culture because of neurogenesis or induction of expression. We will determine if changes occur also in 1) ORN electrophysiological properties, 2) ORN cilia and 3) the presence of sustentacular cells. We will determine if regulation of OMP expression is specific to olfactory cells. A particular goal will be to determine if OMP expression is regulated by cell contact or a soluble factor(s). We will define an assay system for future investigation of regulatory molecules.